1. Field of the Invention
The present invention relates to a power-generation control device and a power-generation control method for a hybrid vehicle, for controlling an internal combustion engine, an electric motor, a battery, and an in-vehicle electric load which constitute a power-generation system of the hybrid vehicle so that a temperature rise of the electric motor is suppressed.
2. Description of the Related Art
The following hybrid vehicle technology to reduce a fuel consumption amount of an automobile is generally known. Specifically, an electric motor is provided on an output shaft of an internal combustion engine so as to compensate for a low-thermal efficiency portion of the internal combustion engine with a driving force of the electric motor and to recover deceleration energy generated at the time of deceleration of the automobile by the electric motor as regenerative power.
The above-mentioned hybrid vehicle, which is operated by the combination of power of the internal combustion engine and power of the electric motor, additionally requires a battery as compared with a vehicle using only the power of the internal combustion engine. In current general hybrid vehicles, an about 100- to 300-V battery is mounted in order to drive the electric motor. Specifically, a large battery is required to be mounted so as to reduce the fuel consumption amount.
Therefore, in recent years, hybrid vehicles compliant with a 48 V-battery which is smaller than those of conventional hybrid vehicles have been proposed. This proposition is also encouraged by situations in which a 12-V battery mounted in conventional vehicles cannot supply sufficient power to an in-vehicle electric load for an automobile, which requires large power.
However, the electric motor for assisting drive of the internal combustion engine is required to have a high torque. In general, the high-torque electric motor has a large induced voltage constant. Therefore, an induced voltage of the electric motor becomes large when an rpm of the electric motor becomes higher. As a result, there is a problem in that the induced voltage of the electric motor adversely exceeds an allowable voltage of the 48-V battery.
As a technology for reducing the adverse effects of the increase in induced voltage of the electric motor on the battery as described above, there exists a method of suppressing an induced-voltage rise by controlling a field-weakening current to flow through the electric motor (see, for example, Japanese Patent Application Laid-open No. 2000-354305).
However, the related art has the following problem.
Specifically, according to Japanese Patent Application Laid-open No. 2000-354305, in order to protect the battery, the field-weakening current is required to be controlled to flow through the electric motor to suppress the induced-voltage rise. However, there is a fear in that the temperature of the electric motor is disadvantageously increased by the field-weakening current to cause an electric motor failure.